PHOTOS: '20/20: A Barbara Walters Special'

Barbara Walters Progeria

Lindsay Ratcliffe of Flat Rock, Mich., lives inside a body that is biologically older than that of her grandmother. The 7-year-old is one of 80 known children who suffer from progeria, an extremely rare and fatal disease characterized by rapid aging in children. It occurs in 1 of every 4 to 8 million births around the world, according to the Progeria Research Foundation.

Donna Svennevik/ABC

Barbara Walters Progeria

Lindsay Ratcliffe of Flat Rock, Mich., lives inside a body that is biologically older than that of her grandmother. The 7-year-old is one of 80 known children who suffer from progeria, an extremely rare and fatal disease characterized by rapid aging in children. It occurs in 1 of every 4 to 8 million births around the world, according to the Progeria Research Foundation.
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Donna Svennevik/ABC

Barbara Walters Progeria

At birth, Lindsay showed no signs of progeria. Four months later, when she had gained little weight, her parents Kristy and Joe Ratcliffe said they knew something was seriously wrong. It took doctors six weeks to diagnose Lindsay with progeria -- a fatal disease where children on average die at 13.
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"In the beginning it was a lot harder because she couldn't talk and she couldn't walk and she couldn't do everything for herself. Now, it's so easy because you see her and you smile. You can't help it," Kristy Ratcliffe said about her vibrant daughter.

Donna Svennevik/ABC

Barbara Walters Progeria

Barbara Walters met Lindsay Ratcliffe and her family in May 2010. At times, Lindsay is another first grader, who loves playing with ponies, Legos and running. But her physical limitations make it hard for her to keep up with her classmates.
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"Whether it's T-ball or basketball, she will sit there and will give it 110 percent no matter what. She knows that she's not the fastest out there in T-ball, but it doesn't stop her," Joe Ratcliffe said. "She might not come in first place, but she is there. It's all heart."

Donna Svennevik/ABC

Barbara Walters Progeria

Lindsay is one of 9 girls in the U.S. who has progeria. Amazingly, Kaylee Halko, 8, who has the same rare condition, lives an hour away in Monclova, Ohio. The two girls are close friends and because of progeria look strikingly similar. They both get upset when they're mistaken for babies.

Donna Svennevik/ABC

Barbara Walters Progeria

Barbara Walters Progeria

Even though she's only three feet tall and 24 pounds, Kaylee's three older brothers -- TJ, 12; Brendan, 10, and Jacob, 8 -- describe her as fearless with a larger-than-life personality.
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"She's very outgoing. She can talk to just about anybody," T.J. told Walters. "We really don't think about her having a disease. We just think of her as a normal person."

Donna Svennevik/ABC

Barbara Walters Progeria

For parents Marla and Tim Halko, it's important for Kaylee to live a full and happy life like normal kids. The pint-sized girl attends cheer dance school to feed her love of dance, and rides the school bus with her peers. Kaylee is pictured with her parents and Barbara Walters.